Strain-induced pseudomagnetic field and photonic Landau levels in dielectric structures

Magnetic effects at optical frequencies are notoriously weak, so magneto-optical devices must be large to create a sufficient effect. In graphene, it has been shown that inhomogeneous strains can induce 'pseudomagnetic fields' that behave in a similar manner to real ones. Here, we show experimentally and theoretically that it is possible to induce such a field at optical frequencies in a photonic lattice. To our knowledge, this is the first realization of a pseudomagnetic field in optics. The field yields 'photonic Landau levels' separated by bandgaps in the spatial spectrum of the structured dielectric lattice. The gaps between these highly degenerate levels lead to transverse optical confinement. The use of strain allows for the exploration of magnetic-like effects in a non-resonant way that would be otherwise inaccessible in optics. It also suggests the possibility that aperiodic photonic-crystal structures can achieve greater field enhancement and slow-light effects than periodic structures via high density of states at the Landau levels. Generalizing these concepts to systems beyond optics, such as matter waves in optical potentials, offers new intriguing physics that is fundamentally different from that in purely periodic structures.